Prior to the general election, the primary election in February 2010 featured extremely close races between candidates for the two largest parties' nominations. Quinn warded off a challenge by Comptroller Dan Hynes by a margin of about 8,300 votes, while Brady won the Republican nomination on the strength of less than a 200-vote margin in a fractured seven-way race.

Pat Quinn (Democratic) (campaign website[permanent dead link]): Incumbent governor who assumed office after the impeachment of Rod Blagojevich; sought a full term in 2010.[1] Quinn was previously Revenue Director for the City of Chicago, State Treasurer (1990-1994), and an unsuccessful candidate for the Democratic nomination for U.S. Senator (1996), Illinois Secretary of State (1994), and Lieutenant Governor (1998).

Scott Lee Cohen (Independent): Former Democratic nominee for Lieutenant Governor in 2010 who was replaced by Sheila Simon after withdrawing due to allegations of abuse toward his wife and other charges. Cohen was reported to have been in a private meeting with Speaker Michael Madigan discussing his plan for running against Quinn.[12]

This section needs expansion. You can help by adding to it.(February 2010)

After the February 2 Democratic primary in which incumbent Governor Pat Quinn was re-nominated, attention was drawn to Scott Lee Cohen, the Democratic nominee for Lieutenant Governor. Illinois law required that candidates for Governor and Lieutenant Governor run in separate primary elections, but run as a ticket in the November general election. Cohen was criticized for his having been charged with domestic battery, in which he was accused of holding a knife to the throat of an ex-girlfriend who was also a convicted prostitute. Cohen was also accused by his ex-wife of physical abuse and using illegally obtained anabolic steroids.[13] Quinn and Dick Durbin, Illinois's senior U.S. Senator, both said that Cohen should withdraw his candidacy,[14][15] which he did on February 7.[16] Cohen ran as an independent candidate for the office of Governor against Quinn.[12]

Even though Brady won 98 out of the 102 counties, Quinn narrowly prevailed. Brady won almost everywhere in the state. Brady even won all of the Chicago collar (suburban) counties. However Quinn's huge win in Cook County which encompasses the Chicago Metropolitan Area, proved too much for Brady to overcome. Quinn initially had a large lead when results first began to come in. This is due to the fact that heavily populated areas tend to report their votes faster. Once the more suburban and rural areas came in Brady narrowed the gap, to a very close race, but once again Cook County proved too much for Brady to overcome. Brady conceded defeat later the following day on November 3, when it became clear he would lose. Quinn's win was ranked by Politico as the 7th biggest upset of the 2010 elections. This was also unique in the fact that this marked one of the very few times that the Democrats had won the governor's office in Illinois three consecutive times in a row.